Bots can solve captchas more accurately and more efficiently than humans. For example, I use the browser extension Captcha Buster to solve Google Captchas for me. Nowadays websites instead use proof-of-work "captchas", which require the visitors' devices to solve cryptographic challenges (similar to bitcoin mining). This is why they sometimes takes a few seconds to complete (even more on low end smartphone / battery saving mode). But even those only slow down, not prevent bot access.